Flow-through capacitors have proven commercially useful for water purification and are well represented in the patent literature. For example, U.S. Pat. No. 3,658,674, issued Apr. 25, 1972; U.S. Pat. No. 5,192,432, issued Mar. 9, 1993; U.S. Pat. No. 5,196,115, issued Mar. 23, 1993; U.S. Pat. No. 5,200,068, issued Apr. 6, 1993; U.S. Pat. No. 5,360,540, issued Nov. 1, 1994; U.S. Pat. No. 5,415,768, issued May 16, 1995; U.S. Pat. No. 5,425,858, issued Jun. 20, 1995; U.S. Pat. No. 5,538,611, issued Jul. 23, 1996; U.S. Pat. No. 5,547,581, issued Aug. 20, 1996; U.S. Pat. No. 5,620,597, Apr. 15, 1997; U.S. Pat. No. 5,748,437, issued May 5, 1998; and U.S. Pat. No. 5,779,891, issued Jul. 14, 1998. The flow-through capacitors of the prior art become less energy efficient with increased solution concentration, and lose energy with concentrated solutions, including seawater. Therefore, the need exists for an improved flow-through capacitor with increased energy and weight efficiency, useful for purification concentrated solutions over 2000 ppm, including desalination of seawater, as well as more dilute solutions with increased energy efficiency.